Super-weak RF connection

[S1500]

Okay, so I have my Colecovision with the A/V jacks out. Those work great. But are there any tips on using RF connections on my other 2 CVs? I can assume the RCA cables that originally came with them(that I still have) are probably past their useful life.

 

I used a standard RCA cable(the usual A/V ones) to plug into the adaptor, then into the coaxial cable, then into the VCR. I also tried going directly to the TV, but wow...

 

It's just...flakey. Look at it wrong and the signal goes out(past any threshold of "signal" for a TV or VCR to pick up before it bluescreens) or it's really snowy.

 

Is there any fix one can do cheaply? Is it a matter of maybe some soldering/clean-up work in the console, or putting an RF shield core around the RCA cable?